Ecological studies on migratory polymorphism of rice pests, a skipper Parnara guttata and the small brown planthopper, Laodelphax striatellus were conducted in relation to the influence of environmental factors and genetical basis. P. guttata has flight polymorphisms which are determined by photoperiods. It has three generations a year and adults of the 2nd generation is well known to migrate. to south western direction in autumn. The flight activity and preoviposition perio were compared among the polymorphic adults which correspond to each of the 3 generations. The adults corresponding to the 2nd generation have higher flight activity and longer preoviposition period then those corresponding to the 1st generation. Furthermore, the adults which correspond to the overwintering generation also have the migrant traits. Therefore, the adults which emerge after hibernation may also migrate as well as the adults of the 2nd generation.The small brown planthopper L. striatellus has wing dimorphism, macroptery and brachyptery. The genetic strains were established by selection for wing forms for more than 15 generations. Crossing between the two strains showed that the genetic basis of the wing dimorphism is not a simple Mendelian but is polygenic, and the quantitative genetic model assuming the character threshold explained well the crossing data. The minimum number of genes concerning the wing form determination was estimated as 2.07, and the realized heritability for macroptery was estimated as 0.36. The color variations of adults and photoperiod sensitivity in terms of nymphal development were also heritable characters. Both characters varied density-dependently as well as the wing dimorphism did. The three characters as mentioned above correlated each other. Therefore, the three characters are supposed to be regulated by a common physiological factors such as JH hormone and genetic basis of them also are supposed to be common.